[Digikam-users] faulty profiles in /usr/share/apps/libkdcraw/profiles folder

[Elle Stone]

Back in January, 2013 I filed a bug report
(https://bugs.kde.org/show_bug.cgi?id=312551) that Showfoto wasn't
properly opening camera-generated jpegs that had ColorSpace tags
instead of an embedded ICC profile, IF the ColorSpace tag indicated
that the image should be AdobeRGB instead of sRGB (sRGB images open
properly).

Has anyone else encountered this bug? I think I figured out the
problem, but it's not in the code that reads the embedded metadata
tags. The problem seems to be that showFoto assigns this faulty
profile:

/usr/share/apps/libkdcraw/profile/adobergb.icm

There are six profiles in /usr/share/apps/libkdcraw/profiles:
adobergb.icm, applergb.icm, prophoto.icm, srgb.icm, srgb-d65.icm, and
widegamut.icm. All of these profiles are available to be assigned to
images opened by digiKam and Showfoto. You can also convert an image
to these profiles, or choose them as your default working space.

The reason I'm posting here as well as the bug report is because on my
computer (running Gentoo, digiKam/showFoto 3.3 and libkdcraw-4.10.5),
three of these profiles -  adobergb.icm, applergb.icm, and srgb.icm -
are faulty because they contain unadapted primaries (see
http://brucelindbloom.com/, scroll down to the section called "Adapted
Primaries") and so really shouldn't be used for image editing.

If you **assign** one of these faulty profiles to an image, often the
fact that there's an issue will be obvious because the image will
acquire a blue color cast. But if you **convert** an image to one of
these profiles, the only way you'll know there's a problem is if you
eyedropper what should be a neutral gray color and find out that the
RGB values don't match, which can create problems while image editing
(for example, trying to color balance the image).

I've attached a profileless test jpeg that is solid white (all RGB
values are 255,255,255). Regardless of what working space profile you
assign to this test jpeg, it should look solid white. But if you
assign adobergb.icm, applergb.icm, or srgb.icm from the
/usr/share/apps/libkdcraw/profile/ folder, the test image will look
blue-green.

The other three profiles - prophoto.icm, srgb-d65.icm, and
widegamut.icm - are OK to use. The widegamut profile has a 256-point
TRC instead of a proper gamma=2.2 TRC, but at least it's useable. It
would be better to change it to a proper gamma=2.2 TRC.

Elle
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